New reports reveal alleged south Florida shooter Nikolas Cruz was actually on the FBI’s radar, students joked he would quote “shoot up the school” one day, and his step-mom died of the flu.

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A 19-year-old man armed with an AR-15 rifle and described as a former student carried out a shooting Wednesday afternoon that left 17 people dead at a south Florida high school in Parkland, according to the Broward County sheriff.

Hours after a shooting rampage at Marjory Stoneman Douglas High School in Broward County Wednesday ...more

Hours after a shooting rampage at Marjory Stoneman Douglas High School in Broward County Wednesday afternoon, parents were waiting for their children outside the school (pictured) as well as at the Coral Springs Marriott.

XAVIER MASCAREÑAS/TCPALM

It was one of the deadliest mass shootings to take place in Florida since the June 12, 2016 Pulse Nightclub shooting in Orlando that left 49 victims dead.

This massacre — which happened on Valentine's Day — was one of the deadliest to happen on a school campus in U.S. history.

According to law enforcement sources, the shooter, former student Nikolas Cruz, was captured after an intense manhunt of the campus grounds. He had been expelled from the school for disciplinary reasons, the sheriff reported.

"I'm saddened to say that 17 people lost their lives."- Sheriff Scott Israel #stonemanshooting

It was near dismissal time as hundreds of students were preparing to leave Marjory Stoneman Douglas High School in Broward County when a fire alarm was pulled and gunshots from the high-powered rifle rang out. The shooter wore a gas mask, according to U.S. Sen. Bill Nelson, speaking on CNN.

Within moments, more than a dozen people — including students — were wounded and hundreds of students were scrambling for safety as bullets sprayed the hallways. Students hid in classrooms, not sure of what was happening as the loud sounds of gunfire continued.

Rebecca Bogart, 17, wasn’t sure if the reports of shooting were a drill.

Her high school had a fire drill earlier that day, and she knew it was somewhat common to do an active shooter drill.

It wasn’t until the windows of her first-floor classroom shattered and Bogart saw a bullet near the shades did she understand what was happening.

Superintendent Robert W. Runcie shares a message regarding today’s tragedy at Marjory Stoneman Douglas High School. @RobertWRuncie says “There are no words to express the sorrow that we are all feeling.” Read the full message: https://t.co/1ETFwGw5Gl

Bogart said that’s what she and her classmates tried to do as they hid from the shooter.

Though she couldn’t see them from under the teacher’s desk where she was hiding, Bogart said she could hear four of her classmates screaming in pain from injuries.

She didn’t know if they had been shot.

When the SWAT team entered the room, they escorted the students out. As Bogart walked down the hall, she saw students covered in blood.

The SWAT team told her and her fellow students to get as far away as possible. Bogart said she walked miles before stopping to get picked up by her father.

“I’m still in shock right now,” she said.

'Catastrophic'

Authorities immediately offered a grim assessment of what happened.

"It's catastrophic. There really are no words," Israel said in a news conference nearly two hours after the shooting took place.

Helicopter footage shortly before 4 p.m. showed police frisking a handcuffed young man outside a squad car. Dressed in a maroon shirt and dark trousers, he was placed in the squad car as TV choppers filmed the scene. He gave no visible sign of being injured, but authorities said Cruz was transported to Broward Health North.

Broward Health spokesperson Jennifer Smith said the hospital had nine patients, including Cruz, who is no longer there. Two of those patients died, three are in critical condition and four are in fair condition.

Dr. Benny Menendez, chief of emergency medicine at Broward Health Medical Center, said the hospital received seven victims: five are stable and two are critical.

"So far, we have at least 14 victims. Victims have been and continue to be transported to Broward Health Medical Center and Broward Health North hospital," the Broward County Sheriff's office tweeted just over an hour after being called to the site.

Media reports from the school showed images of hundreds of students frantically running — at times walking with their hands up — from the campus. Armed deputies, including tactical team members in armored vehicles and carrying assault rifles, could be seen guiding students from the school.

The school had gone on lockdown. Hundreds of students were released a short time later.

Nikolas Cruz, a classmate who participated in Davis’ ninth-grade JROTC group, was usually a quiet kid who kept to himself, but “there was a lot of anger management issues there,” she said.

“Finding out it was him him makes a lot of sense now,” Davis said.

Cruz would joke about shooting people or shooting up establishments, she added. At the time, she thought it was normal, violent teenage jokes. Cruz would also talk a lot about having guns and using them in different situations, she said.

It was the latest in a series of mass shootings to take place in the U.S. this year.

There have been six school shootings since Jan. 1 involving injuries or deaths to students. In all, 18 school shooting incidents have taken place, according to the advocacy website Everytown for Gun Safety, which has logged or counted 290 school shootings since 2013. That included everything from suicides to mass shootings.

Sandy Hook, Pulse nightclub, Ft. Lauderdale airport, Las Vegas and now Parkland, Florida - when is this going to stop? It’s not going to stop until the American people say: enough is enough! What is it going to take for enough to be enough? pic.twitter.com/SVJzvlJzsR

Sheriff Scott Israel of Broward County says the 19-year-old suspect is in custody and that investigators are beginning to "dissect" what happened in the attack Wednesday at Marjory Stoneman Douglas High School in Parkland. (Feb. 14)

AP

Reactions

The devastating scene of panicked students fleeing the school and a ring of deputies surrounding the campus prompted prayers and words of comfort from national and state leaders.

President Donald Trump contacted Gov. Rick Scott about the shooting.

“My prayers and condolences to the families of the victims of the terrible Florida shooting,” Trump tweeted Wednesday afternoon. “No child, teacher or anyone else should ever feel unsafe in an American school,” the president wrote.

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Members of the Florida House had a moment of silence while they were in session and were getting constant updates from the floor.

State Sen. Kevin Rader, who represents the area, is heading back to his district, according to a Senate Democrats’ tweet.

Broward's public school district is the sixth largest in the nation. There are 3,158 students attending the high school, according to the National Center for Education website.

Brevard Public Schools Superintendent Desmond Blackburn previously worked in the Broward County school district. "My thoughts and prayers are with the entire school system. It’s a horrific incident," Blackburn said in a statement to FLORIDA TODAY.

Before coming to Brevard in June 2015, Blackburn worked there as an area superintendent and area director of school improvement, principal of Ramblewood Middle School in Coral Springs, assistant principal of Sunrise Middle School in Fort Lauderdale and a math teacher at Plantation High School in Plantation.

Sen. Lauren Book, D-Plantation, represents Broward and talked about the impact of such incidents.

“We hear about school shootings all the time. Sadly, they have become a part of our national news cycle. As a mom and a former classroom teacher, I am left more and more horrified and agonized with each tragedy," she said.

"And yet, despite the seemingly endless reports, nothing prepares you for the reality of a school shooting unfolding in your own community. I am devastated. Fellow parents, let’s all hug our babies a little closer tonight.”

Alexandra Schmitz and Caroline Glenn with the USA TODAY Network and The Associated Press contributed to this report.